The present invention generally relates to simulating recloser pole positions in a recloser control, and more specifically, to a permanent three-pole independent pole operation recloser simulator feature in a single-pole trip capable recloser control.
Electric utility systems or power systems are designed to generate, transmit and distribute electrical energy to loads. In order to generate, transmit and distribute electrical energy, power systems generally include a variety of power system elements such as generators, transformers, power lines, buses and capacitor banks. As a result, power systems must also include protective devices and procedures to protect those elements from electrical short circuits. Such protective devices and procedures react to short circuits by isolating the short circuit from the remainder of the power system.
The short circuit faults may be caused by a number of conditions, for example, a conductor falling on the ground, a tree coming in contact with a conductor or two conductors touching each other. Further the conditions may be “self-healing” or they may be permanent. A self-healing or temporary short circuit is a short circuit that ceases to exist if power is removed from the short circuit for a period of time. Power system protection engineers take advantage of this fact by designing protective schemes that use automatic reclosers. Automatic reclosers re-energize a faulted element some time after it has been de-energized in response to a short circuit. If the short circuit is temporary (i.e., if it has self-healed during the time it was de-energized) then power is automatically restored sooner via operation of the automatic recloser. If the short circuit is not self-healing, then the automatic recloser will act again to isolate the short circuit from the remainder of the power system. One such automatic recloser is simply called a recloser.
Reclosers are fault interrupting devices that may combine fault detection, fault current interruption and subsequent line closing functions in one piece of equipment. Reclosers are typically utility pole-mounted on lower voltage (i.e., less than 40 kilovolt (KV) overhead distribution lines and feeders. Much like a circuit breaker, a current interrupting mechanism (“interrupter”) of the recloser enables de-energizing and re-energizing of one phase of a three-phase (“3-phase”) power signal. De-energizing is accomplished when the interrupter (e.g., a set of contacts) interrupts, or breaks, a high current flow during an occurrence of a short circuit. Re-energizing is accomplished when the interrupter makes, or re-establishes, the current flow.
Generally, an individual interrupter is part of a pole assembly, or pole, of the recloser. Each pole corresponds to one phase of the three-phase power system and may further include a chamber housing the interrupter and providing required insulating and arc interrupting medium (e.g., SF6 gas, oil), and an auxiliary contact mechanically linked to the interrupter. The auxiliary contact operates to provide an indication of the interrupter's open or closed status, referred to hereinafter as an open or closed pole status.
A single-phase trip capable recloser is sometimes referred to as an Independent Pole Operation (IPO) recloser. Older three-pole trip capable reclosers (“3-pole reclosers”) were not capable of independent pole operation. As a result, the three interrupters of the older 3-pole reclosers were opened and closed together, even if only one phase of the three-phase power system was short circuited, such that all three phases were either energized or de-energized. Recent 3-pole recloser designs include three independent poles each having an interrupter operable to selectively and independently de-energize a corresponding phase of a three-phase power signal. Such reclosers are referred to herein after as 3-pole IPO reclosers. After opening a single pole in response to a single phase short circuit, the recloser re-energizes the corresponding phase (i.e., the recloser closes one pole) by either a self contained mechanical means of the recloser or by command from an external recloser controller, or recloser control.
A recloser control is typically mounted in a weather-proof enclosure at the bottom of a utility pole or steel structure to control and monitor operation of an associated recloser. Recloser controls are often capable of monitoring and controlling more than one pole of a recloser. For example, some recloser controls are capable of controlling a 3-pole IPO recloser, where the recloser control can independently open and close each pole's interrupter.
Prior to installation, recloser control testing requires connection to an actual recloser or to a bulky testing unit designed to simulate operation of a recloser. Recloser control testing with an actual recloser may not be practical due to recloser size or availability in a test lab setting. Further, recloser control testing with a testing unit requires that the testing unit be capable of exact simulation of the recloser. In the case of a 3-pole IPO recloser, recloser control testing requires that the testing unit be capable of receiving the trip (open) and close signals from the recloser control and be capable of emulating the three independently operated poles of a 3-pole IPO recloser. Moreover, for 3-pole IPO reclosers having magnetic actuators requiring a common trip and close circuit capable of dual polarity (i.e., direct current is applied in one direction to trip an interrupter, and in the opposite direction to close it), suitable test sets may not be available.
In the absence of suitable external testing or simulation equipment, one alternative is to utilize the recloser control to simulate the open and close pole states of the 3-pole IPO recloser. Prior art methods include building a temporary internal simulator using programmable logic. After testing is complete, the logic for temporary internal simulator is removed to prevent erroneous pole position indications during actual recloser operation in a power system. Unfortunately, use and removal of the temporary internal simulator logic may introduce erroneous logic settings into the recloser's existing correct logic, and may result in recloser control malfunction in the power system.